US11740445B2 - Advanced optical designs for imaging systems - Google Patents

Abstract

An eye-mounted device includes a contact lens and an embedded imaging system. The front aperture of the imaging system faces away from the user's eye so that the image sensor in the imaging system detects imagery of a user's external environment. The optics for the imaging system has a folded optical path, which is advantageous for fitting the imaging system into the limited space within the contact lens. In one design, the optics for the imaging system is based on a two mirror design, with a concave mirror followed by a convex mirror.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent application Ser. No. 16/895,077, “Advanced Optical Designs for Eye-mounted Imaging Systems,” filed Jun. 8, 2020; which is a continuation-in-part of U.S. patent application Ser. No. 16/034,761 now U.S. Pat. No. 10,712,564, “Advanced Optical Designs for Eye-Mounted Imaging Systems,” filed Jul. 13, 2018. The subject matter of all of the foregoing is incorporated herein by reference in its entirety.

BACKGROUND1. Technical Field

This disclosure relates generally to imaging optics, for example as may be used with an eye-mounted imaging system.

2. Description of Related Art

Handheld cameras are ubiquitous. A large fraction of the world's population carries smartphones and most smartphones have one or more cameras. This allows people to document their lives and experiences. Pictures and videos of epic events, spectacular vacations and lifetime milestones are routinely captured by handheld cameras. At the other end of the spectrum, the number of selfies, cat videos and pictures of mediocre meals has also exploded in recent years.

Body-mounted cameras or body-cams go one step further. They automatically go where the user goes and can automatically record what the user is experiencing. Head-mounted or helmet-mounted cameras go even one step further. They automatically view what the user is viewing or, at least where he turns his head. They can record events from this point of view.

However, all of these imaging devices are separate pieces of equipment that are visible to others. They are also relatively large and are not carried on the user's eye.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure have other advantages and features which will be more readily apparent from the following detailed description and the appended claims, when taken in conjunction with the examples in the accompanying drawings, in which:

FIG.1A shows a user wearing an eye-mounted device in communication with an auxiliary necklace.

FIG.1B shows a magnified view of the electronic contact lens mounted on the user's eye.

FIG.2 shows a cross sectional view of an electronic contact lens with an embedded imaging device (femtoimager).

FIGS.3A-3C show cross sectional views of a femtoimager optical system, with possible ray paths to the center, right edge and left edge of the image sensor, respectively.

FIGS.4A and4B show perspective views of a femtoimager optical system.

FIG.5 shows a cross sectional view of an eye-mounted device with a femtoimager and a femtoprojector.

FIG.6 shows a cross sectional view of another femtoimager optical system.

FIG.7 shows a cross sectional view of yet another femtoimager optical system.

FIG.8 shows a cross sectional view of a horizontally positioned femtoimager in a contact lens.

FIG.9 shows a cross sectional view of yet another femtoimager in a contact lens.

FIG.10A shows a cross-sectional view of yet another femtoimager, with possible ray paths to the left edge, center and right edge of the image sensor.

FIG.10B shows extraneous rays blocked by baffles in the femtoscope ofFIG.10A.

FIG.11A shows a cross-sectional view of yet another femtoimager.

FIG.11B shows reflected extraneous rays blocked by baffles in the femtoscope ofFIG.11A.

FIGS.12-15 show cross-sectional views of additional femtoimagers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures and the following description relate to embodiments by way of illustration only. It should be noted that from the following discussion, alternative embodiments of the structures and methods disclosed herein will be readily recognized as viable alternatives that may be employed without departing from the principles of what is claimed.

An eye-mounted device includes a contact lens and an embedded imaging device, which for convenience is referred to as a femtoimager because it is very small. The front aperture of the femtoimager faces away from the user's eye so that the image sensor in the femtoimager captures imagery of a user's external environment. In various embodiments, the femtoimager operates in a visible wavelength band, a non-visible wavelength band, or a combination of both.

The femtoimager optics has a folded optical path, which is advantageous for fitting the femtoimager into the limited space within the contact lens. In one design, the optics for the femtoimager is a two mirror design, with a concave primary mirror followed by a convex secondary mirror in the optical path from the front aperture to the image sensor. In some embodiments, the optical system includes a solid transparent substrate with the primary mirror formed on one face of the substrate and the secondary mirror formed on an opposing face of the substrate. The front aperture is annular and may be axially positioned between the two mirrors. It may include a lens or other refractive interface. Light blocking structures, light-redirecting structures, absorbing coatings and other types of baffle structures are used to reduce or eliminate extraneous light from reaching the image sensor.

The eye-mounted device may include other components in the contact lens: a projector that projects images onto the retina, other types of sensors, electronics, batteries, a coil to wirelessly receive power, or an antenna to transmit/receive data, for example. These components may be positioned in front of the pupil in the optical path of the eye. Some components must be positioned within this optical zone, for example in order to project images onto the retina. Other components may be positioned outside the optical zone. The femtoimager may be either within or outside the optical zone.

In more detail,FIG.1A shows a user wearing an eye-mounteddevice105 in communication with anecklace106.FIG.1B shows a magnified view of the user's eye and eye-mounted device. The eye-mounteddevice105 includes acontact lens110 that is worn on the surface of the eye. The following examples use a scleral contact lens but the contact lens does not have to be scleral. Thecontact lens110 contains afemtoimager120. Thefemtoimager120 captures images of the external environment.

FIG.1B shows a front view of thecontact lens110 mounted on a user's eye. Thecontact lens110 is placed on the surface of the eye. Thecontact lens110 moves with the user's eye as the user's eye rotates in its socket. Because thefemtoimager120 is mounted in thecontact lens110, it also moves with the user's eye. The ratio of the contact lens diameter to femtoimager lateral size is preferably roughly 15:1. This ratio is normally between about 15:1 and 30:1, but may be as small as 5:1 or smaller or as large as 50:1 or larger.

In this example, thecontact lens110 also containselectronics140 and a coil (or antenna)145. In some embodiments, thecoil145 is a power coil that receives power wirelessly, for example via magnetic induction. In other embodiments, thecontact lens110 includes a battery that supplies power to thefemtoimager120. Theelectronics140 may be used to control the femtoimager, receive or process images from the femtoimager, provide power to the femtoimager, and/or transmit data to/from the femtoimager. Thecontact lens110 may also include other components, such as a projector that projects images onto the user's retina (referred to as a femtoprojector).

FIG.1A shows an implementation where, in addition to the eye-mounteddevice105, the user is also wearing anecklace106 that contains components of the eye-mounted system. In this example, thenecklace106 includes awireless transceiver107 that transmits/receives image data and/or transmits power to the eye-mounteddevice105. Image transmission to/from an eye-mounted device is subject to data rate constraints due to size and power consumption limitations of electronics in a contact lens. Off-lens accessory devices may be used in place of, or in addition to, a necklace.

FIG.2 shows a cross sectional view of thecontact lens110 with embeddedfemtoimager120.FIG.2 shows an embodiment using a scleral contact lens but thecontact lens110 does not have to be scleral. Thecontact lens110 preferably has a thickness that is less than two mm. Thefemtoimager120 preferably fits in a 1 mm×1 mm×1 mm volume, or at least within a 2 mm×2 mm×2 mm volume. Thecontact lens110 is comfortable to wear and maintains eye health by permitting oxygen to reach thecornea150.

For completeness,FIG.2 shows some of the structure of theeye100. Thecontact lens110 is separated from thecornea150 of the user'seye100 by a tear layer. The aqueous of the eyeball is located between the cornea and thecrystalline lens160 of theeye100. The vitreous fills most of the eyeball. Theiris180 limits the aperture of the eye.

Thefemtoimager120 is outward-facing, meaning thefemtoimager120 “looks” away from theeye100 and captures imagery of the surrounding environment. The field ofview125 of thefemtoimager110 may be the same, smaller or larger than a field of view of the user's eye. As shown in more detail below, thefemtoimager110 includes imaging optics (referred to as a femtoscope), a sensor array and sensor circuitry. The sensor array may be an array of photodiodes. In some embodiments, the sensor array operates in a visible wavelength band (i.e., ˜390 nm to 770 nm). Alternatively or additionally, the sensor array operates in a non-visible wavelength band, such as an infrared (IR) band (i.e., ˜750 nm to 10 μm) or an ultraviolet band (i.e., <390 nm). For example, the sensor array may be a thermal infrared sensor.

The sensor circuitry senses and conditions sensor signals produced by the sensor array. In some instances, the output signals produced by the sensor circuitry are analog signals. Alternatively, the sensor circuitry may include analog-to-digital converters (ADC), so that the output signals are digital rather than analog. The sensor circuitry may also have other functions. For example, the sensor circuitry may amplify the sensor signals, convert them from current to voltage signals or filter noise from the sensor signals to keep a signal-to-noise ratio below a threshold value. The sensor circuitry may be implemented as aseparate electronics module140. Alternatively, it may be implemented as a backplane to the sensor array. Processing of the images captured by the femtoimager may occur outside thecontact lens110.

FIGS.3-4 show an example femtoimager design.FIGS.3 and4 show cross sectional views and perspective views, respectively, of a femtoimager. The femtoimager uses a femtoscope with two mirrors that direct incoming light to animage sensor340. The femtoscope ofFIG.3 includes a solid,transparent substrate310. The solidtransparent substrate310 may be made from plastic, glass or other transparent materials. The femtoscope also includes an annular concaveprimary mirror360 and a convexsecondary mirror350. Either or both of these may be aspheric. The concaveprimary mirror360 may be formed by coating an end of thesubstrate310 with a reflective material such as a metal (e.g. aluminum or silver) or an engineered stack of dielectric layers. The shape of theprimary mirror360 may be made by any of several different techniques. For example, if the substrate is injection-molded plastic, then the shape of theprimary mirror360 follows the shape of the mold used. Alternatively, the shape of theprimary mirror360 may be made by diamond turning the substrate on a lathe. Or, the shape of theprimary mirror360 may be made by photolithography and etching steps. Gray scale photolithography may be used to etch a mirror surface profile, for example. Wafer scale optics techniques including embossing, compression molding and/or UV curing photosensitive polymers may also be used to form mirror profiles. Additive manufacturing or three-dimensional printing (e.g. via two-photon polymerization) techniques may also be employed. These techniques may also be used to form thesecondary mirror350.

Theprimary mirror360 includes a clear, non-reflective back aperture365 (also referred to as the output aperture). Animage sensor340, such as an array of photodiodes, is mounted at this location. Other types of image sensors include phototransistors, CCDs, pyrometer-based sensors, micro-bolometers, and sensors based on vanadium oxide, silicon, indium phosphide, gallium antimonide or gallium arsenide, for example.

Thesecondary mirror350 faces theprimary mirror360, and theimage sensor340 faces thesecondary mirror350. Light rays enter the femtoscope through the front aperture370 (also referred to as the input aperture). They are first incident on and reflected by the annularprimary mirror360. The reflected rays are then incident on and further reflected by thesecondary mirror350 before exiting through theback aperture365 and reaching theimage sensor340. Theprimary mirror360 andsecondary mirror350 cooperate to form an image of the external environment, which is captured by theimage sensor340.

Theprimary mirror360 andsecondary mirror350 cooperate to image rays entering through thefront aperture370 onto theimage sensor340. However, not all light rays from the external environment are included in image formation. Those light rays that are used to form an image are referred to as image-forming rays. The remaining light rays are referred to as extraneous rays. InFIG.3, thefront aperture370 is annular in shape (but not required to be planar). It is defined by aninner edge372 andouter edge374. Thefront aperture370 limits which rays enter the optical system to form the image. In this design, thefront aperture370 is not axially aligned with either of themirrors350,360. That is, the z-coordinate of thefront aperture370 is between that of theprimary mirror360 and thesecondary mirror350. InFIG.3, thefront aperture370 is located approximately midway between the twomirrors350,360.

The system also includes a light baffle system to block or at least reduce extraneous light. InFIG.3, the baffle system includes aninner baffle382 which serves as a three-dimensional obscuration, and a side baffle with anexternal portion384 and aninternal portion386. The baffles may be either an integral part of the femtoscope or a surrounding structure in which the optical system is mounted. Absorbing or black baffles may also make the femtoimager less visible to others. In one implementation, theobscuration382 andinternal side baffle386 are made by depositing an absorbing material such as carbon, roughened or etched nickel (“nickel black”), black chrome, or Vantablack (Surrey NanoSystems, Newhaven, UK) on thetransparent substrate310, which serves as the core of the optical system. Black indium-tin oxide may also be used. Theexternal side baffle384 may be separate from thesubstrate310, for example, it may be an absorbing material deposited on the sides of a hole into which the core is inserted during assembly.

InFIG.3, the baffle system is designed to block all extraneous rays that would have a direct path from the external environment to theimage sensor340. Accordingly, theobscuration382 extends an entire length between thesecondary mirror350 and theinner edge372 of the front aperture. Theexternal side baffle384 extends from theouter edge374 of the front aperture away from theprimary mirror360 and is sufficiently long to block all extraneous rays that would propagate through thefront aperture370 directly to theimage sensor340. Although not required inFIG.3, it may be extended to an edge that is axially aligned with thesecondary mirror350 without adding length to the overall system. Theinternal side baffle386 extends an entire length from theouter edge374 of the front aperture to theprimary mirror360. In other embodiments, the baffle system may block less than all of the extraneous rays, so the baffles may be shorter.

FIG.3A shows possible ray paths to the center point of theimage sensor340. These ray paths may be classified as follows. The bundle ofrays341 are reflected by theprimary mirror360 and thesecondary mirror350 to form the image on theimage sensor340. These are the image-formingrays341. InFIG.3A, the image-formingray bundle341 is labelled both as it enters through thefront aperture370 and as it propagates from thesecondary mirror350 to theimage sensor340.

The remaining paths are possible paths for extraneous rays, which are managed as follows. Extraneous rays that might have propagated along the ray paths inbundle345 to theimage sensor340 are blocked by the back side of thesecondary mirror350. Extraneous rays are prevented from reaching the possible ray paths in bundle346 (between the solid ray and the dashed ray) by theobscuration382 andsecondary mirror350. Extraneous rays are prevented from reaching the possible ray paths in bundle347 (between two dashed rays) by theexternal side baffle384. The possible ray paths inbundle348 are blocked by theinternal side baffle386. For clarity, only the lefthand rays are marked inFIG.3A, but a similar situation exists for the righthand rays. Similar diagrams may also be produced for other points on theimage sensor340.

FIGS.3B and3C show possible ray paths to the two edge points of theimage sensor340. The extraneous rays are managed in a similar fashion as described inFIG.3A. The edge points ofFIGS.3B and3C also lead to the following considerations. Again, consider only the lefthand rays. InFIG.3B, theexternal side baffle384 is tapered outwards (or otherwise shaped) from theouter edge374 of the front aperture so that it does not block the outermost image-formingray341X.Ray341X passes through theouter edge374 of the front aperture and is incident on the farthest point of theimage sensor340. As a result, it is propagating at the outermost angle of all image-forming rays. Ifexternal side baffle384 does not blockray341X, it also will not block any of the other image-forming rays. In addition, as shown inFIG.3C, theexternal side baffle384 is long enough to prevent extraneous rays from reachingray path347A. Becauseray path347A passes through theinner edge372 of the front aperture to the outermost edge of theimage sensor340, it will intersect theside baffle384 at the farthest possible axial distance from theimage sensor340.

Also inFIG.3C, theobstruction382 andinternal side baffle386 are shaped so that they do not block either image-formingray341Y or341Z.Ray341Y passes through theinner edge372 of the front aperture and is incident on the nearest point on theimage sensor340. As a result, it is propagating at the innermost angle of all image-forming rays. Ifobstruction382 does not blockray341Y, it also will not block any of the other image-forming rays. InFIG.3, the three-dimensional obstruction382 is the combination of an annulus next to thesecondary mirror350 plus a conical frustum that extends the entire length between the annulus and theinner edge372 of the front aperture.

FIGS.4A-4B show perspective views of the femtoscope fromFIG.3.FIG.4A shows just thecoated substrate310. Theinternal side baffle386 is cylindrical in shape (i.e., the sides are parallel to the optical axis of the system). Theobstruction382 is a frustum plus a narrow annulus, which is adjacent to thesecondary mirror350. Thefront aperture370 is the transparent annulus between theinternal side baffle386 and three-dimensional obstruction382. In some designs, thefront aperture370 has an axial location that is closer to midway between the primary and secondary mirrors, than to either theprimary mirror360 or thesecondary mirror350. For example, if z is the axial dimension and the two mirrors are located at z=0 mm and z=1 mm, then the front aperture is located in the range 0.25 mm<z<0.75 mm. The primary mirror and the back aperture for the image sensor are on the back face of the substrate, which is not visible inFIG.4A.FIG.4B also shows theexternal side baffle384.

As noted above, the design inFIGS.3-4 blocks all extraneous rays that would propagate directly to theimage sensor340. However, this is not strictly required. Thedifferent baffles382,384,386 do not have to extend the entire lengths shown. They may be shorter in some designs. For example, theobstruction382 may occupy some of the space between thesecondary mirror350 and theinner edge372 of the front aperture, but without extending that entire length. It may extend from thesecondary mirror350 towards theprimary mirror360 but without reaching theinner edge372 of the front aperture. Similarly, theexternal side baffle384 may extend from theouter edge374 of the front aperture, but may not be long enough to block all direct ray paths through thefront aperture370 to theimage sensor340. The same is true for theinternal side baffle386. In some cases, there may not be aninternal side baffle386 if the oblique extraneous rays are weak or managed by another mechanism.

Thebaffles382,384,386 also do not have to have the shapes shown. For example, any absorbing structure that extends from the edge of thesecondary mirror350 to theinner edge372 of the front aperture without blocking the image-formingrays341 shown inFIG.3C may serve the same purpose as theobstruction382 with the shape shown inFIG.3. Different shapes may have advantages in manufacturing or assembly.

As a final set of variations,FIGS.3B-3C show some situations where certain image-formingrays341 should not be blocked by the baffles. However, this is not strictly required. Blocking some of the image-formingrays341 may be acceptable in some designs.

The design of femtoimagers is complicated by constraints such as the very small volume in which the system must fit, refractive indices of the substrate and the surrounding contact lens material, and required optical magnification specifications. The size and curvature of the primary and secondary mirrors, the size of the image sensor, and the indices of refraction are all examples of parameters that may be adjusted by an optical designer to optimize different design priorities such as optical throughput, depth of focus, field of view, magnification and resolution.

In some designs, theimage sensor340 is not more than 500 microns wide. For example, theimage sensor340 may be a 500×500 array of sensors, with a sensor-to-sensor pitch of not more than 3 microns and preferably not more than 1 micron. A 500×500 array with 1 micron pitch is approximately 500 microns on a side. An array with 500×500 color pixels using a Bayer pattern is less than 1 mm on a side using 1 micron pitch individual sensors (with three or more individual sensors per color pixel). Image sensors may be other sizes. For example, infrared sensors may be significantly larger. Sensor-to-sensor pitches of 10, 20 or even 40 microns are possible.

Some designs may have a narrow field of view, such as 2 degrees or less. The two-mirror design shown inFIGS.3-4 is suited for narrower fields of view (for example, in the range of 5 to 15 degrees) and correspondingly higher resolutions. Larger and smaller fields of view are also possible with the two-mirror design.

The specific design of the femtoimager depends on the application. For non-imaging applications, the actual resolution may be lower than used for imaging applications. For example, a femtoimager with a small number (e.g., 10×10 array) of relatively large pixels may be used as a sensor for eye tracking applications. The femtoimager may view a far-away object, or a closer reference object such as the user's nose.

The design shown inFIGS.3-4 utilizes a folded optical path. As a result, the optics have an optical path that is longer than the thickness of the contact lens. This may result in lower aberrations and higher angular resolutions. The optical path allows the image sensor to be oriented approximately parallel to, rather than perpendicular to, the contact lens surfaces. The femtoimager may occupy not more than 1 to 2 mm of vertical space (i.e., contact lens thickness) and/or the femtoimager may have a lateral footprint of not more than 2 to 4 mm². The front aperture may have a maximum lateral dimension of not more than 1 to 2 mm.

In addition to capturing images of the external environment or providing eye tracking functionality, femtoimagers may also be used for other applications in different types of eye-mounted devices. For example,FIG.5 shows a cross sectional view of an eye-mounted device with afemtoimager120 and a femtoprojector530 (i.e., a small projector also contained in the contact lens110). Thefemtoimager120 captures images within its field ofview125. The femtoprojector530projects images595 onto theretina590 of the user. These two may be coordinated so that the images captured by the femtoimager are used to determine theimages595 projected by thefemtoprojector530.

FIGS.6-12 show additional variations of the femtoscope ofFIG.3. These variations involve internal refractive interfaces, obscuration position and shape, and other parameters. The design choices are necessarily illustrated in combinations and, to keep the number of figures under control, not every possible combination is shown. For example, the choice of shape of internal refractive interface is largely independent of the choice of obscuration location or obscuration shape. Some combinations of those choices are illustrated. Those skilled in the art will appreciate that other, unillustrated combinations may be desirable in certain situations.

The design ofFIG.6 is also based on atransparent substrate610, with theimage sensor640 andprimary mirror660 on one face and thesecondary mirror650 on an opposing face. However, the three-dimensional obscuration682 is formed by creating a groove in the core material and then coating the interior of the groove with an absorbing material. Apartial side baffle684 is similarly created.

The design ofFIG.7 includes aplanarization fill712. If thecore material710 has refractive index n₁, thefill material712 has a different refractive index n₂, and the surrounding material (e.g., the contact lens material) has refractive index n₃, then there are two refractive interfaces. The first is at theexit aperture770. The secondrefractive interface714 is between thefill material712 and the surrounding material. These refractive interfaces may be shaped to achieve various optical functions, for example introducing optical power or correcting optical aberrations. The other numbered elements inFIG.7 are the same as the numbered counterparts inFIG.3:image sensor740, convexsecondary mirror750, concaveprimary mirror760,inner baffle782, side baffleexternal portion784 and side baffleinternal portion786.

InFIG.2, a femtoimager is shown mounted in a contact lens in a “vertical” configuration. The optical axis and/or axis of symmetry of thefemtoimager120 is approximately perpendicular to the outer surface of thecontact lens110. InFIG.8, thefemtoimager820 is mounted in a “horizontal” configuration. The optical axis and/or axis of symmetry of the femtoimageroptical system830 is approximately parallel to the outer surface of thecontact lens110. In this configuration, aturning mirror840 directs image rays from the external environment to the femtoimageroptical system830.

FIG.9 shows a cross sectional view of yet another femtoimager in acontact lens110. The assembly ofFIG.9 has the following structure. Acavity950 is formed in thecontact lens110 and thesolid core910 shown inFIG.4A is inserted into thecavity950. In this example, thecavity950 tapers inwards from the outer surface of the contact lens and then has straight sidewalls where it contacts thecore910. The sidewalls of thecavity950 are absorbing. This may be achieved by coating the sidewalls of the cavity. Alternatively, alarger hole940 may first be formed and filled with dark colored epoxy942 (Master Bond EP42HT-2MED Black, for example). Thecavity950 is then formed in the epoxy. The remaining darkcolored epoxy942 serves as the absorbing side baffle for the femtoimager. Materials other than epoxy may be used. Its sides may be coated instead, for example.

FIG.10A shows a cross-sectional view of yet another femtoimager, with ray paths to the left edge, center and right edge of the image sensor.FIG.10A is drawn to scale and the femtoscope is approximately 0.7 mm in diameter. In this example, the femtoscope includes a solid,transparent substrate1010 with anannular input aperture1070 and anoutput aperture1065. Theinput aperture1070 is approximately axially aligned with the convexsecondary mirror1050, and theoutput aperture1065 is approximately axially aligned with the concaveprimary mirror1060. Theinput aperture1070 may form a refractive interface and it may be curved or otherwise shaped to improve the imaging performance. Theinput aperture1070 and mirrors1050,1060 may be aspheric. In this example, theimage sensor1040 is slightly separated from theoutput aperture1065. Here, the spacing (shown as a rectangle inFIG.10A) is a glue layer to attach theimage sensor1040 to theoutput aperture1065.

FIG.10A shows the ray paths for image-formingrays1041 from theinput aperture1070 to theimage sensor1040, for rays incident on the left edge, center and right edge of the image sensor. Image-forming rays from the input aperture to other locations on the image sensor will fall within the boundaries defined by the rays shown inFIG.10A. The aggregate of all image-forming rays may be divided into three ray bundles: afirst bundle1041A of image-forming rays propagating from theinput aperture1070 to theprimary mirror1060, asecond ray bundle1041B propagating from theprimary mirror1060 to thesecondary mirror1050, and athird ray bundle1041C propagating from thesecondary mirror1050 to the output aperture1065 (and then on to the image sensor1040).

InFIG.10A, there are two spaces between these image-forming ray bundles. Onespace1078, which will be referred to as the input interspace, is located between the first and second ray bundles1041A and1041B. InFIG.10A, theinput interspace1078 is stippled because it is empty space. There is no material in theinput interspace1078. Theother space1068, which will be referred to as the output interspace, is located between the second andthird ray bundles1041B and1041C. Theoutput interspace1068 is indicated by the dotted triangle inFIG.10A. The interior of the triangle is not patterned because the output interspace is filled with the substrate material. Baffles may be positioned in these two interspaces to control extraneous rays without interfering with image-forming rays. For convenience, these will be referred to as the input baffle and output baffle, respectively. In the example ofFIG.10A, the input baffle is a groove in thesolid substrate1010 with two absorbing surfaces:outer surface1081A which is adjacent to thefirst ray bundle1041A, andinner surface1081B which is adjacent to thesecond ray bundle1041B. Theoutput baffle1086 is a flat absorbing ring in this example. It is positioned in theoutput interspace1068, but does not extend into the interspace as a groove would. The femtoscope design also includes aside baffle1089.

FIG.10B shows operation of the baffle system in blocking extraneous rays. The femtoimager has a field of view and rays within the field of view are imaged onto theimage sensor1040. Rays outside the field of view that enter theinput aperture1070 are blocked by the baffles.

Consider first the rays that enter theinput aperture1070 at theouter edge1074. Refraction at the input aperture is ignored inFIG.10B for purposes of illustration. Rays in thebundle1042 are outside the field of view of the femtoimager, and these rays are blocked by theouter surface1081A of the input baffle. Rays inbundle1043 are also outside the field of view and are blocked by theoutput baffle1086.Bundle1041A contains the image-forming rays. Now consider the other extreme of rays entering theinput aperture1070 at theinner edge1072.Ray bundle1046 is blocked by theside baffle1089. Rays inbundle1041B are the image-forming rays.FIG.10B shows rays in the plane of the cross-section. For a femtoscope design that is axially symmetric, skew rays will behave similarly by applying the above analysis to the radial component of each skew ray. Note that all extraneous rays that would have a direct path from theinput aperture1070 to theimage sensor1040 are blocked by either theinput baffle1081A or theoutput baffle1086.

FIG.11A shows a cross-sectional view of yet another femtoimager.FIG.11A shows the same set of rays as inFIG.10A. The femtoscope design inFIG.11A is the same as inFIG.10A, except that the output baffle is not an annular ring. Rather, it is a groove with two absorbing surfaces:outer surface1186A andinner surface1186B. As shown inFIG.11A, this design of the output baffle does not block any of the image-forming rays, so the design is non-vignetting. However, it does block additional paths of extraneous rays to theimage sensor1040. Absorbing surfaces are not completely absorbing, so some low fraction of the incident light will be reflected off the baffle surfaces. As shown inFIG.11B, residual reflection ofextraneous rays1142 off theside baffle1089 would be directed to theimage sensor1040. Theouter surface1186A of the output baffle blocks these once-reflectedextraneous rays1142 from reaching the image sensor.

FIG.12 shows a cross-sectional view of yet another femtoimager that blocks additional extraneous rays. As shown inFIG.11B, a small portion ofextraneous ray1143 from outside the field of view may be reflected byinner surface1186B to theimage sensor1040. InFIG.12, theinner surface1286B of the output baffle is angled to reflect these residualextraneous rays1143 away from theimage sensor1040 rather than towards it. Theinner surface1286B of the output baffle may vignette some of the image-forming rays.

FIG.13 shows a cross-sectional view of yet another femtoimager. InFIG.13, the side baffle includes acurved section1389A, followed by astraight section1389B. In this design, thecurved section1389A is defined by an ellipse with twofoci1372 and1373. The three-dimensional shape is an elliptical toroid.Focus1372 is the inner edge of theinput aperture1070.Focus1373 is the tip of theouter surface1286A of the output baffle. Every ray that enters the femtoscope throughfocus1372 and propagates to theelliptical section1389A is primarily absorbed, but there may be some residual reflection to theother focus1373. This design prevents these residual reflections from then propagating directly to theimage sensor1040.

Consider two points along thecurved section1389A as examples. First,ray1343 enters throughfocus1372 and hits the bottom point of theelliptical section1389A. The non-absorbed portion ofray1343 is reflected to focus1373, and theouter surface1286A of the output baffle blocks it from reaching theimage sensor1040. For allother rays1344 that enter through theinput aperture1070 and hit the same bottom point ofsection1389A, reflected light is reflected at a shallower angle and therefore also will be blocked from reaching theimage sensor1040 after only one reflection. The same construction can be made for any other point on theelliptical section1389A. For example,ray1345 is another ray that enters throughfocus1372 and hits theelliptical section1389A somewhere along its length. Reflected light is reflected to focus1373. For allother rays1346 that enter through theinput aperture1070 and hit the same point on theelliptical section1389A, reflected light is reflected at a shallower angle and therefore also will be blocked from reaching theimage sensor1040 after only one reflection. Thestraight section1389B is angled to also prevent reflected rays from propagating directly to theimage sensor1040. Theellipse1389A plusstraight section1389B is just one possible design. Other shapes and curves may also be used to ensure that once-reflected rays do not have a direct path to theimage sensor1040.

FIGS.14-15 show cross sectional views of additional femtoimagers. These figures show the use of additional refractive interfaces in the femtoscope. In bothFIGS.14 and15, the image-forming rays from the distant object propagate along optical paths that enter the solidtransparent substrate1010 with index n₁, reflect off theconcave mirror1060, reflect off theconvex mirror1050, and exit the substrate through a central opening (output aperture1065) to theimage sensor1040. The femtoscope operates at near infinite conjugate ratio. Theimage sensor1040 is close to theoutput aperture1065 of the substrate. The femtoscope may also contain baffles—input baffles, output baffles and/or side baffles—as described previously.

InFIGS.14-15, the rays refract at interface(s) before entering thesubstrate1010, as described in more detail below. InFIG.14, solidtransparent material1412 with index n₂≠n₁creates a firstadditional interface1472 with thesubstrate1010. For example, index n₁may be greater than 1.5, while index n₂is less than 1.5. The difference between n₁and n₂may be greater than 0.1. InFIG.15, solidtransparent material1512 with index n₃≠n₂creates a secondadditional interface1572. These interface(s) may be used to improve the image quality of the femtoscope.

The use ofintermediate material1412 inFIG.15 may improve the optical power that may be achieved, because the refractive indexes n₁and n₃may be close to each other. Thesubstrate1010 may have a high index n₁. Index n₃may also be high in order to match the contact lens material, or it may in fact be the actual contact lens material. Therefore, without an intermediate lower index material, the difference between indexes n₁and n₃may be low, which would then require a more severely shaped interface in order to achieve a desired refractive effect.

InFIG.15, theintermediate material1412 is introduced and index n₂may be chosen to be significantly lower than both n₁and n₃so that theinterfaces1472,1572 have more optical power to correct the image-forming rays. For example, both n₁and n₃may be 1.5 or greater for the reasons given above. If n₂is selected to be 1.4 or less, then the difference in refractive index at each interface will be at least 0.1. In some embodiments,material1512 may be Zeonex or acrylic and material1412 may be silicone (PDMS) or low index UV-curable adhesives (e.g. from Norland).Interface1472 may be concave or convex and is generally aspheric.Interface1572 may be flat or curved.Exit surface1574 may be convex spherical, with radius of curvature similar to the contact lens or cornea.

Theintermediate material1412 is encapsulated between thesubstrate1010 and theouter material1512. It could be something other than a solid, but solid materials have advantages over gases and liquids.Material1512 interfaces to the rest of the contact lens. In some cases,material1512 may be the contact lens material, so thatexit surface1574 is the exterior surface of the contact lens. If not,material1512 may have the same index as the contact lens material.

InFIG.15,material1512 is shaped with aprotrusion1590, as is material1412 inFIG.14. The device shown inFIG.15 is not the finished optical system. Rather, it is a precursor to the final device. Theprotrusion1590 may be used to facilitate handling of the precursor and then removed either before or after assembly into the contact lens. For similar reasons, even if theexit surface1574 is not the final exterior surface of the contact lens, it may have the same shape as the final surface to facilitate testing of the optical system.

A variety of femtoimager optical systems (femtoscopes) have been described. Each of them may be made small enough to fit in a contact lens using plastic injection molding, diamond turning, photolithography and etching, or other techniques. Most, but not all, of the systems include a solid cylindrical transparent substrate with a curved primary mirror formed on one end and a secondary mirror formed on the other end. Any of the designs may use light blocking, light-redirecting, absorbing coatings or other types of baffle structures as needed to reduce stray light.

When a femtoimager optical system is described as “cylindrical”, its cylindrical shape may include a flat on a sidewall. In other words, the circular cross section of a perfect cylinder is not a requirement, just an overall cylindrical shape. Optical systems may also be made from extrusions of other shapes, such as triangles, squares, pentagons, etc.

Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples. It should be appreciated that the scope of the disclosure includes other embodiments not discussed in detail above. For example, the designs above all use solid substrates, but an air core may also be used. As another example, although the femtoimager is described as embedded in a contact lens, small imaging devices may also be used in other applications, such as embedded in an eyeglasses lens, used in endoscopes, or mounted on drones. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope as defined in the appended claims. Therefore, the scope of the invention should be determined by the appended claims and their legal equivalents.

Claims (20)

What is claimed is:

1. A femtoscope optical system comprising:

a solid transparent substrate comprised of a transparent first material having a refractive index n₁;

a concave mirror positioned to a first side of the substrate, the concave mirror having a central opening;

a convex mirror positioned to a second side of the substrate and opposite the central opening;

a solid transparent second material having a refractive index n₂, positioned to the second side of the substrate; and

a solid transparent third material having a refractive index n₃, also positioned to the second side of the substrate, the second material positioned between the third material and the substrate, the second material and substrate forming a first interface with n₂≠n₁, and the third material and second material forming a second interface with n₃≠n₂;

wherein the optical system projects image-forming rays from a first conjugate to a second conjugate; and the image-forming rays propagate along optical paths that originate from the first conjugate, refract at the second interface, refract at the first interface, enter the substrate, reflect off the concave mirror, reflect off the convex mirror, and exit the substrate through the central opening.

2. The optical system ofclaim 1 wherein the optical system operates at a near infinite conjugate ratio.

3. The optical system ofclaim 1 wherein a distance from the central opening to the second conjugate is less than a distance from the convex mirror to the central opening.

4. The optical system ofclaim 1 wherein n₁−n₂≥0.1 and n₃−n₂≥0.1.

5. The optical system ofclaim 1 wherein n₁≥1.50, n₃≥1.50, and n₂≤1.45.

6. The optical system ofclaim 1 wherein n₁and n₃are closer to each other than to n₂.

7. The optical system ofclaim 1 wherein the second material comprises silicone.

8. The optical system ofclaim 1 wherein the second material comprises an adhesive.

9. The optical system ofclaim 1 wherein the third material is one of acrylic or Zeonex.

10. The optical system ofclaim 1 wherein the optical system is contained in a contact lens, and the third material is part of the contact lens.

11. The optical system ofclaim 1 wherein the optical system is contained in a contact lens, and a refractive index of the contact lens is substantially equal to n₃.

12. The optical system ofclaim 1 wherein the first interface and the second interface are both curved.

13. The optical system ofclaim 1 wherein the second interface is planar.

14. The optical system ofclaim 1 wherein the optical system is a precursor for assembly into a contact lens, and a surface of the third material opposite the second interface has a same shape as an exterior surface of the contact lens.

15. The optical system ofclaim 1 wherein the optical system is a precursor for assembly into a contact lens, and the third material is shaped with a protrusion.

16. The optical system ofclaim 1 further comprising an input baffle and an output baffle.

17. The optical system ofclaim 1 wherein the optical system is small enough to be mounted in a contact lens.

18. The optical system ofclaim 1 wherein the optical system is small enough to be contained within a 2 mm×2 mm×2 mm volume.

19. The optical system ofclaim 1 wherein the concave mirror and convex mirror contact the substrate.

20. The optical system ofclaim 1 wherein the substrate is plastic or glass.

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